The present invention relates generally to spreader frames used for lifting containerized cargo and more specifically to an improved latching mechanism for attaching the spreader to the container.
In recent years, considerable attention has been directed to development of equipment that is capable of lifting and transporting cargo that is enclosed in containers. These containers have become fairly well standardized being 8 feet wide, 8 feet high and of varying length such as 20, 24, 30, 35 or 40 feet. In order to facilitate efficient handling of these containers of varying length, another international standardization has taken place in that the containers have corner castings at each of the corners provided with an aperture for receiving a locking device or latching mechanism that is mounted on the spreader frame.
The most widely used container has a standard corner casting which conforms to a standard developed by the International Organization for Standardization (ISO Standard) in which all of the castings have an identical size aperture therein and the transverse spacing between the two corner members at each end of the container have a nominal center to center spacing laterally of 89 inches (224.5 centimeters). Another well known type of standard container may have the same general dimensions as indicated above and the corner castings have apertures which are of a different size and configuration and this type of container is commonly known as the "Sealand" container (Sealand Standard). In addition to having a different configuration for the apertures for Sealand Standard, the adjacent corner castings also have the apertures spaced from each other by a center to center dimension of 90 inches (227 centimeters). Thus, the apertures in the corner castings for these two standards are not equidistantly spaced from each other and require a coupling mechanism having different dimensions.
In recent years numerous proposals have been made for the development of a universal latching mechanism which can be used with both the ISO Standard and the Sealand Standard containers. Examples of such latching mechanisms are disclosed in U.S. Pat. Nos. 3,368,838; 3,749,438; 3,751,096; 3,753,588; and 3,799,601. A further type of prior art latching mechanism that has previously been used for accommodating containers with different standard fittings consists of an enlarged ball on the end of the locator which surrounds the shank of the latching member with the enlarged ball being received into a spherical opening in the frame to accommodate universal movement of the free end of the shank with respect to the frame.
While numerous types of latching mechanisms have been proposed for accommodating containers with both ISO Standard and Sealand Standard, none of these mechanisms have received any remarkable degree of commercial acceptance for various reasons. So far as presently known, the only two types of commercial universal latching mechanisms for accommodating containers with ISO and Sealand castings are disclosed in U.S. Pat. Nos. 3,753,588 and 3,749,438. The latching systems disclosed in both of these patents operate on the same common principal of having the rotatable shank or locking member located on a fixed axis and the center to center spacing of the free ends of an adjacent pair of shanks on one end of a spreader is fixed. The variations in the size of the apertures for the two standards is accommodated by the configuration of the latching lugs and/or the size thereof. In both types of latching mechanisms, the surface contact between the casting and the bearing lugs is rather minimal which in some instance may result in having the latching members slip out of the aperture while the container is being lifted. Another problem encountered with the devices of this type is the fact that no provision is made for accommodating for any slight misalignment of the latching lugs with the apertures as the spreader is being aligned with the container. Thus, if the casting member is slightly defective or distorted on the container, it may be impossible for the operator to insert the fixed lugs and shanks into the respective apertures.
It has also been proposed to mount the free end of the latching mechanism for some limited movement such as disclosed in U.S. Pat. Nos. 3,751,096 and 3,677,599. However, these proposed solutions have not been accepted commercially and it is assumed the lack of acceptance can be contributed to the inability of these systems to withstand the abuse encountered during use.